Electron beam modulator



N 1946-, A. L. SAMUEL 2,410,840

I ELECTRON BEAM MODULATbR Filed lay a, 1 42 some l I 2 Off; l g 203 L. K140 I I a I3 m; m

I i I 2 i i INVENTOR A. LSAMUEL BY ncrnon n Monroe Arthur L. Susi, .S I

mit, N. 1., assignor to Belt Teiephone Laboratories, Incorporated, New

YormN. 2., a corporation of'New York Application May 6, 19d2,-Serlai No. 441,937

"5 Claims. .(ci. 250-) This invention relates to electronic devices, particularly for operation at ultra-high frequencies.

An object of the invention is to intermodulate waves of difierent frequencies by virtue of nonlinear actions in a system comprising an electron stream associated with a plurality of electrodes, particularly in frequency shifting arrangements for radio repeaters, first and second detectors in superheterodyne receiving systems, and the like.

Another object of the invention is .to facilitate the omration and tuning of amplifiers, oscillators and the like, especially those employing resonating chambers or cavity resonators.

A feature of the invention is a system to effect frequency conversion employing an electron beam and one or more resonating chambers, in which the output is obtained at the frequency of a local energy source.

Other features include fine adjustment and broad-band tuning arrangements for a resonating chamber.

- This application includes subject matter originally disclosed in my copending application, Serial No. 112,067,, filed September 24, 194:1.

Further objects and features of the invention will be apparent from the following detailed description and the accompanying drawing, while the scope of the invention is defined in the appended claims,

The single figure of the drawing represents a preferred embodiment of the invention.

Referring to the drawing, an evacuated, in-

sulating envelope I is represented as enclosing a plurality of elements including a suitable source of'an electron stream such as an electron gun or beam projector shown generally at 2, and anelec tron intercepting electrode or collector 3. The electron gun 2 is provided with an electron. 'e'mit-' ting cathode 9 which may be associated with any suitable heating means energized, in the embodimen-t illustrated, through leads I0 and by a source ii of electromotive force. Associated with. the cathode Q there may bean electrode I3 for use in regulating and varying the current of the electron beam and commonly known as an accelerating electrode. It may be adjacent to and coaxial with the cathode.

A plurality of conductive discs M I to-2l1 inclusive are hermetically sealedinto and through the envelope l in any known manner. The discs are. spaced at suitable intervals along the path of the electron stream as hereinafter described, and each is provided with a. central aperture in alignment with the axis of the electron gun 2 in order to accommodate the passage of the-electron str from said gun to the collector 3. A pair of adjacent discs 2 and 2I2 respectively form parts of opposing walls of an input resonator I20. The

disc 2" may have attached thereto a short tube 2I8 aligned with the aperture and extending outwardly with'respect to the walls of the resonator I20, The disc 2I2 has fastened to the edge. of the aperture therein a relatively long,- flaring tube :22. longitudinally of the path of the electron stream'a gap I2! isdefined between the central h portion of the inner surface-of the disc 2 and the small and of the tube I22. The disc 2| 3 has fastened to the edge of the aperture therein a ring-shaped electrode. I24 positioned adjacent to the large end of the tube I22. An annular gap I23 is defined between the adjacent ends of the tube I22 and the electrode I24. A pair of adjacent discs 28d and 2I5 respectively form parts of opposing walls of an intermediate resonator I28. The'disc 2H4 supports a flaring tube I20 similar. to but inverted with respect to the tube I22 with the large end of the tube I26 defining together with the upper edge of the electrode I24 an annular gap I25. The disc 2I5 may have, attached to its outer side and surrounding the aperture, a short tube 2I9. A gap I21 is central portion of the inner surface ofthe disc 2 I5 and the small end of the tube I26.

' The walls of the resonator I20 should be conductive, or should at leasthave conductive inner surfaces. The tubes'l22, I26, 2I8 and N9 and the ring I26 should be conductiveand should be conductively fastened to their respective supporting discs.

The portion of the arrangement so far dey scribed is similar to one disclosedand claimed in my copending application Serial No. 388,031, filed April 11, 1941, and assigned to the assignee of the present application. The resonator I20 may be Separated from the gap I21 by a suitable drift.

spacel 29 is a gap I30 which is defined by opposed truncatedconical portions of the discs M6 and 2H. These-discs form portions of the walls of a resonator, e. g., a quarter wave-length coaxial conductor system 208, which mayhave a tuning branch209. A sourcello of alternating potendefinedbetween the Coupling be-' 3 tials is connected with the electrode I24, the direct potential of electrode I24 being maintained at a relatively low potential with respect to the cathode by a source I4I, whereas the conductive portions of the resonators I20,

serve to define the short-circuited end or voltage node of the quarter wave-length line 208, another branch 2I0 being provided for connection to any suitable load.

In the operation of the system shown in the drawing, the input wave, the carrier frequency I28 and 208 and the collector 3 are maintained at a relatively high nection with the resonator I20.

of which will be designated 11 and which wave may bear signals in the form of modulations, e. g., amplitude modulations, is resonated in the chamber I20 and produces an electron velocity variation in the electron stream as the latter traverses the associated gap I2I'. The frequency of the wave supplied by the local source I40 will be designated f2. Electron velocity sorting takes place within the tube I22 due to the influence-of the relatively low potential of the electrode I24. With proper selection or adjustment of the bat-'v tery potentials, a condition is readily secured in which the faster electrons pass through the space within the electrodes I24 and I26 whereas the slower electrons are deflected and intercepted by the electrodes I22, I24 and I26, the result being shown a precise or fine tuning arrangement, comprising a branch cavity 202 of relatively small dimensions, shown broken open, in which is slidably mounted a piston I53 which may be moved by means of a suitably connected knob I54. A similar arrangement may be employed in con- The branch cavity 202 is preferably of such restricted dimensions compared with the main cavity that the resonant frequency of the main cavity is close to and somewhat below the range of free transmission of the branch cavity so that the latter will not fully support a wave of the frequency to be resonated. Then a relatively large motion of the piston I53 will produce only a relatively small change in the resonant frequency of the combination. The currents flowing in the branch cavity will be less than in the main cavity with the result'that any losses associated with the sliding contacts between the piston I53 and the walls of the cavity 202 will be minimized.

The resonator I20 is provided with adjustable side cavities 203 and 204 for the purpose of enabling the resonator to respond to a relatively wide frequency band. The side cavity 203 is coupled to the main cavity by means of an aperture 205 and is adjustable by means of a piston a charge density variation both in the stream of electrons which pass beyond the tube I26 and in the current intercepted by the electrodes. The degree of velocity sorting and resultant group: ing produced is, however, in the present system, under the control of the local source I by virtue of the variable potential superimposed upon the direct current biasing potential of the electrode I24 which causes the resultant bias to fluctuate. Upon passing the gap I2'I, the densityvariedv electron stream serves to excite electromagnetic oscillations in the resonator I28, which resonator may be tuned to respond to one or both of the frequencies (f +f2) and (ii-f2), to reinforce these frequencies which, it will be noted, are modulation products separated from the frequency of resonator I20 by an amount equal to the value of the frequency of the source I40. Oscillations thus produced in resonator I28 impress a corresponding velocity variation upon the electron stream as the latter traverses the gap I21. The velocity variation of the electron stream entering the drift space I29 will contain a component of the local frequency f2 of source I40 bearing the signal modulations of the original incoming wave of frequency ii. The velocity variation is converted in the draft space I29 into density variations at-the gap I30 by the grouping effect of faster electrons overtaking slower electrons.

The resonant line 208 may be tuned by means of the adjustable branch 209 to the frequency f: of the source I40 and will be excited into forced oscillations by means of the density variations at the gap I30. The output of the line 208 may be led through the branch 2 I0 to a suitable load such as an intermediate frequency amplifier or other utilization means.

In connection with the resonator I28 there is 206 connected to a knob 201. The side cavity 204 is connected to the main cavity and adjustable in a similar manner. The resonator I28 may be similarly equipped. The aperture 205 is preferably of a suitable size to provide a loose coupling between the adjacent chambers. side cavities may be independently adjusted to resonate at the same frequency as the associated main cavity or at slightly different frequencies, producing in either case a broad frequency band or relatively flat transmission characteristic in the well-known manner of coupled resonant circuits of whatever form.

In the operation of the system as above described the resonator I20 is assumed broadly tuned to the frequency f1 of the incoming wave and responsive to the sidebands due to the modulation which the incoming wave may bear. The resonator I28 may be tuned broadly to (fl +19 or (ii-f2) as desired, while the line 20a is tuned to In. It is also feasible to operate by tuning the resonator I28 sharply to one of .the above-mentioned frequencies. In that case, the side chambers, 203 and 204' are not needed and the apertures for coupling the side chambers to the main cavity should be closed. It is, also feasible to operate with the resonator I28 tuned so broadly as to include both (f1+fz) and (fl-f2) in which case the line 208 may be energized at twice the frequency f2 and the length of the line 208 up to the position of the tuning stub should be increased accordingly.

What is claimed is: I

I 1. In a frequency conversion system employing an electron beam device, a source of modulated waves of carrier frequency Ir, a source of The- ' original modulation.

variations upon said beam, means for converting the compound variations of the electron beam so produced into a second succession of electron density variations, and resonating means tuned to the frequency f2 in energy exchanging relation with the electron beam to be energized by components of said second succession of electron density variations which carry substantially the 2. In a frequency conversion system employing an electron beam device, a source of modulated waves of carrier frequency ii, a source of wavesof frequency h, a resonator selectively responsive to the frequency h in energy exchanging relation with the electron beam to impress electron velocity variations upon said beam under the control of modulated waves from said source of said waves of carrier frequency f1, means to impress an electron retarding field of variable potential upon said velocity varied beam under the control of waves from said source of frequency f: whereby the slower electrons are turned back and electron density variationsare thereby developed in the continuing portion of the stream including frequency components of fit): and bearing the said modulations originally carried by the waves of frequency f1, 9. resonator selectively responsive to one of the frequencies (,f1+fz) and (f1f2) in energy exchanging relation with the electron beam to be energized by said electron density variations of the electron beam and, in turn, to impress further electron velocity variations upon said beam, means defining a drift space for converting the compound variations of the electron beam so produced into a second succession of electron density variations, and a resonator for waves of frequency f: in energy exchanging relation with the electron beam to be energized by components of said second succession of electron density variations which carry substantially the original modulation.

3. In a frequency conversion system, means for producing an electron stream, a plurality of resonators coupled to the electron stream in energy exchanging relation and arranged at successive points along the path of the electron stream, the first resonator in order in the direction of flow of said stream being resonant to a given frequency ii, the third resonator in said order being resonant to a. given frequency f2, and the second resonator in said order (fr-f2) variably controllable means located between said first and second resonators to convert velocity variations of the electron stream into charge density variations, a source of waves of the frequency fa, means actuated by waves from said source to variably control said conversion means, and means located between said second and third resonatorsfor the further conversion of velocity variations of-the electron stream into charge density variations.

4. In a frequency conversion system, means for producing an electron stream, a source of modulated waves of carrier frequency f1, means to impress upon said electron stream a velocity varlsaid stream a velocity variation under the control of the said charge density variations, means located beyond the region of said reinforcing means whereby velocity variations are converted into charge density variations, and load means arranged to be excited by modulated charge density variations at a carrier frequency equal to f2.

5. The method of frequency conversion which comprises operating upon an electron stream according to the following steps in the order given: velocity varying said stream under control of a modulated wave of carrier frequency f1, developing duced and using said stream to excite a load circuit at a carrier frequency equal to f: accompanied by substantially the original modulations of said modulated wave of carrier frequency {1 ARTHUR L. SAMUEL.

being resonant to; one of the combination frequencies (h f2) and 

